This invention relates to polyesters, and more particularly to the modification of polyesters to enhance their crystallinity.
Poly(1,4-cyclohexanedimethyl 1,4-cyclohexanedicarboxylate), hereinafter sometimes designated "PCCD" for brevity, is a known polyester; reference is made, for example, to U.S. Pat. No. 2,891,930. It is characterized by such advantageous properties as crystallinity and resistance to weathering under conditions of exposure to ultraviolet radiation. These properties have increased interest in commercialization in recent years.
However, the crystallinity of PCCD is not as high as that of such commercially available polyesters as poly(1,4-butylene terephthalate), or "PBT". While the crystalline melting temperature, Tm, of PCCD is in the range of 225-235.degree. C., a relatively high figure, its temperature of crystallization, Tc, is on the order of 152-171.degree. C. Therefore, its solvent resistance is not as high as might be desired. There is interest in increasing the crystallinity of PCCD, and concomitantly increasing its Tc.
Various researchers have reported increases in the Tc of other polyesters as a result of incorporating amide segments therein. For example, Bouma et al., Polym. Prep., 38, 486 (1997), reports previous work by Van Bennekom demonstrating such a phenomenon as a result of the incorporation in PBT or poly(ethylene terephthalate) of ethyleneterephthalamide or 1,4-butyleneterephthalamide units. Further work has shown that increased crystallinity generally has two requirements: a very uniform copolymer (i.e., one in which the amide units are fairly evenly spaced as opposed to being present in blocks) and the presence of alkylene groups separating the nitrogen atoms which have the same molecular structure as the alkylene groups of the polyester. It was also found that side reactions, including methylation of the diamine corresponding to the amide units, occurred in significant amount during preparation of the amide functionality from a diamine. This was particularly true of the one-pot reaction in which tetramethylenediamine first underwent reaction with dimethyl terephthalate and 1,4-butanediol was subsequently added.
U.S. Pat. No. 2,901,466 discloses the preparation of polyesteramides comprising PCCD units in combination with, for example, 1,6-hexyleneterephthalamide units, the latter being present in proportions on the order of 20 mole percent of the polyesteramide. There is no suggestion, however, of an increase in crystallinity as a result of the presence of amide units.